Heat-treating apparatus



July 4, 1950 E. BAILEY 2,513,778

FEAT-TREATING APPARATUS Filed NOV. 9, 1946 2 Sheets-Sheet l IN V EN TOR.

2 Sheets-Sheet 2 Filed Nov. 9, 1946 [J an L..Baile BY 3 3 FTTORNL'YS.

Patented July 4, 1950 HEAT-TREATING APPARATUS Edgar L. Bailey,Birmingham, Mich., assignor to Chrysler Corporation, Highland Park,Mich. a corporation of Delaware Application November 9, 1946, Serial No.l08,960

7 Claims. 1

This invention relates to heat treating apparatus and moreparticularly-to apparatus designed to combine inductive and conductiveheating.

It is a well known phenomenon that when certain temperatures areattained in metals their magnetic properties diminish. The temperatureat which this occurs is commonly referred to as the Curie point. It isan object of this invention to utilize this phenomenon and by theselection of a proper frequency of magnetic field to inductively heatobjects to their Curie point and then transport them to a conductiveheating means adapted to heat them to still higher temperatures. Thefact that the magnetic properties of the objects diminish at their Curiepoint is utilized to release them from the induction heating system sothat apparatus may carry them into a conductive heating zone forconductive heating to a temperature above their Curi point.

The initial heating by induction is desirable be cause inductive heatingis generally faster than conductive heating and the size of the furnacerequired is less than that of a wholly conductive heating furnace.

A further object of the invention is to provide a conductive heatingapparatus that has a controlled maximum temperature and to provideinterchangeable liners by which this furnace temperature may be altered.

In the drawings:

Fig. l is a vertical elevation of a portion of a furnace embodying myinvention;

Fig. 2 is a continuation in vertical elevation of Fig.1; and

Fig. 3 is an end View taken on the line 33 of Fig. 1 with the hopperomitted.

A base it has a hopper l I supported thereon by members l2. Spacedsupports 13 and M are mounted on base I 0. Supports I3 and M are eachprovided with a plurality of laterally extending shafts l5 preferablythree in number. Each shaft l5 has a roller l6 rotatably mountedthereon. A cylindrical furnace element ll is provided with collars l8and I9 which are concentric thereto. The collar N3 is provided with atrack 20 which is adaped to receive the rollers I6 of the support it.Collar I9 is provided with a circular periphery adapted to engage therollers l6 ofthe support M. The support I3 is provided with a centralopening 2!! which is adapted to receive the furnace element H. Thecylindrical furnace element ii is thus rotatably mounted.

A sprocket or gear 22 is keyed to the collar l8 and adapted to beoperatively connected to suit- 2 able driving means to rotate thecylindrical furnace element. Fig. 3 illustrates a motor 24 as driving asprocket 25 and chain 26. The chain '26 is in driving engagement withthe sprocket 22.

A cylindrical liner 2] is mounted inside the cylindrical furnace elementI! in concentric relationship therewith and is secured thereto by asleeve 23 and the set screws ll and 42. The liner 21 has an axialdimension which is less than the axial dimension of the furnace elementH and is preferably positioned adjacent one end thereof. In Figs. 1 and2 this is illustrated as the right end. A screw element 28 is positionedwithin the liner 2! in coaxial relationship therewith and has anextension 29 which is mounted in a hub 30 formed on the support [4. Asuitable set screw 31 is positioned in engagement with the hub 30 andthe extension 29 to prevent rotation of the screw element 28. Theconstruction thus far described provides a rotatable furnace element Hand a liner 2] and a stationary screw element 28. The furnace element 11is provided with a lateral opening 32 adjacent the right end thereof inFig. 2. The liner 21 is provided with a similar opening 33 which isaligned with the opening 32. A cylindrical insulating element 34surrounds the furnace element ll. This insulating element is preferablystationary.

Suitable electric conductors, preferably in the form of coils of wire35, are arranged in'cylindrical form and positioned around theinsulating element 34. This wire is supported by members 36, 31, and 50which are supported by base ID. A chute 38 is supported b the base belowthe aligned openings 32 and 33 and a similar opening 39 is provided inthe base ID. The openings 32, 33, chute 38 and opening 39 form adischarge passage 40 from the furnace. Any desired quenching apparatussuch as oil tanks may b placed below the base II] in alignment with theopening 39 so that objects which have been heated and discharged fromthe furnace will be directed by discharge passage 40 toward thequenching apparatus.

When an electric current of the proper frequency is sent through thecoils 35 and the magnetic field created thereby is used to inductivelyheat the objects, heat will be imparted to them faster than the heat islost by radiation. Extremely low frequencies are objectionable for theyimpart heat to the objects so slowly that the heat lost by radiationprevents a sufficient temperature rise. When the proper frequencies areused, the temperature will rise until the metal reaches its Curie pointand the magnetic propenquency coupled with the diminished magneticproperties in the objects is then incapable of overcoming radiationsufficiently to heat the objects further. Too high a frequencywillimpart energy to. the objects so rapidly that even the diminishedmagnetic ropertiesjand radiation are insufiicient to prevent acontinued, if less rapid, temperature rise. It has been found thatfrequencies in the range of 180 to 500 cycles per second aresatisfactory with a frequency in the neighborhood of 360 cycles persecondgiving the best results.

In operation, the coils 35 are energized and the motor 2 started. Themotor 24 drives the sprocket 22 and rotates the collar l8, furnaceelement l1, and liner 21. The work pieces which it is desired to heattreat, arepreferably ferrous metal and may be dumped into hopper ll.These work pieca may be 01' various shapes such as ball bearings, nuts.bolts, etc. Ball bearings 5| have been illustrated. Objects 5| to beheat treated will fall by gravity and be drawn by the magnetic fieldthrough the spout 43 and through the opening 44 provided. in the endplate 45 ofthe furnace into the interior of the cylindrical furnaceelement IT. These objects will be magnetized by their presence in themagnetic field created by the electrical conductors 35., The magnetizedobjects when agitated by the rotation of the furnace element I! willtend to accumulate in a large mass in the furnace element II. This massof objects is in the magnetic field of the conductors 35 ,andwili beinductively heated. The magnetic attraction of the objects will retainthem in the mass during this heatin tion of the liner 21. The screwelement 28 will define a path for the objects through the interior ofthe liner 21. This path may be of calculated length so that conductiveheating may be timed. The conductors 35, which are concentric with theliner 21, cause an inductive heating of the liner 21.' The liner 21 isformed from a material such as a cobalt allot which has its Curie pointat a considerably higher temperature than the Curie point of the objectsbeing heat treated. The inductive heating of the liner 2'! may attaintem eratures impossible in.

the inductive heating of the ob ects. The high temperature of the liner21 will by conduction heat the objects as they move around the screwelement 28 to a temperature that is higher than the temperature whichthey possessed upon entering the screw element 28. At intervals when theopening 33 in the liner and the opening 32 in the furnace element arerotated into position below the screw element 28, objects which havecompleted their passage through the furnace will drop therethroughandout of the discharge path 40.

The liner 2! is formed from material which possesses a higher Curiepoint than iron. Cobalt iron alloys have been found to be verysatisfactory materials. age of cobalt included in the alloy change theVariations in the percent 4- Curie point of the liner 21. A plurality ofintel-changeable liners 2! having different percentages of cobalttherein may be selectively used to obtain the desired'temperature oftheliner since the temperature is dependent upon the Curie point.

I claim:

1. In an apparatus for heat treating metal objects possessing magneticproperties, the combination of an elongated furnace element forming apassage, said furnace element having an inlet adjacent one end of saidpassage and an outlet adjacent the other end of said passage, means todeliver said objects to said inlet, a second means forming a first zonein said furnace element adjacent said inlet, said second means beingadapted to simultaneously subject a plurality of said objects to amagnetic field, magnetize and inductively heat said objects until theobjects have attained a temperature substantially corresponding to theirCurie point at which time said objects separate from each other and areno longer efiected by said magnetic field, means forming a second zonein said furnace element positioned between said first zone and saidoutlet, means to transport said objects through said second zone fromsaid' first zone to said outlet and means to conductively heat saidobjects during their travel through said second zone.

2. In an apparatus, for heat treating metal objects possessing magneticproperties, the combination of an elongated furnace element forming apassage, said furnace. element having an inlet adjacent one end of saidpassage and an outlet adjacent the other end of said passage, means todeliver said objects to said inlet, an electrical conductor, means tofurnish electrical energy to said conductor, said electrical'conductorbeing disposed around said furnace element and comprising means toinduce a magnetic field in a portion of said passage adjacent said inletwhereby objects in said portion are retained therein by the magneticheld and are inductively heated until they have attained a temperaturesubstantially corresponding to their Curie point when their magneticproperties diminish and they are released from the magnetic field, meansto transport said released objects from said first portion of saidfurnace and to deliver said objects to said outlet and sup plementalheating means adapted to heat said objects during their travel from saidfirst portion to said outlet and to materially raise the temperature ofthe objects above their Curie point.

3. In an apparatus for heat treating ferrous metal objects havingmagnetic properties the combination of an elongated furnace elementforming a passage, said furnace element havin an inlet adjacent one endof said passage and an outlet adjacent the other end of said passage,means to deliver said objects to said inlet, means disposed around saidfurnace element to create an alternating magnetic field in a portion ofsaid heat said objects by conduction during their travel from said firstportion to said outlet.

4. In an apparatus for heat treating metal objects possessing magneticproperties, the combination of an elongated furnace element forming apassage, said furnace element having an inlet adjacent one end of saidpassage and an outlet adjacent the other end of said passage, means todeliver said objects to said inlet, second means forming a first zone insaid furnace element adjacent said inlet, said second means beingadapted to subject said objects to a magnetic field, magnetize andinductively heat said objects until the objects have attained atemperature substantially corresponding to their Curie point, thirdmeans forming a second zone in said furnace element positioned betweensaid first zone and said outlet, said third means including an elementformed from a metal having a higher Curie point than the objects, meansto inductively heat said element to a temperature higher than themaximum temperature obtainable in the first zone, means to transportsaid objects through said second zone in close proximity to said elementand to deliver said objects to said outlet whereby said objects areheated by conduction from said element during their travel from saidfirst zone to said outlet.

5. In an apparatus for heat treating various metal objects havingmagnetic properties, the

combination of a cylindrical furnace element forming a passage, saidfurnace element having an inlet and an outlet displaced axially fromsaid inlet, a cobalt alloy liner positioned within said cylindricalfurnace element adjacent said outlet whereby a first axial portionadjacent said inlet of said cylindrical furnace element extends beyondsaid cobalt alloy liner and a second axial portion of said cylindricalfurnace element is concentric with said cobalt alloy liner, means todeliver said objects to said inlet, electrical conductors concentricallydisposed around saidcylindrical furnace element, means to transmit analterto its Curie point and the objects being transnating currentthrough said conductors whereby ported through said liner are furtherheated by conduction from said liner.

6. A method of heat treating a plurality of metal objects which havemagnetic properties comprising feeding individual objects into amagnetic zone, magnetizing said objects in said zone and simultaneouslyagitating said objects to accumulate a mass of said individual objectstherein, inductively heating said mass of objects in said magnetic zone'with a current frequency between 180 to 500 cycles per second,continuing said heating until the individual objects become magneticallynonadherent and separate from said mass, and then positively moving theobjects out of said zone.

7. A method of heat treating a plurality of metal objects which havemagnetic properties comprising feeding individual objects into amagnetic zone, magnetizing said objects in said zone and simultaneouslyagitating said objects to accumulate a mass of said individual objectstherein, inductively heating said mass of objects in said magnetic zonewith a currrent frequency between 180 to 500 cycles per second,continuing said heating until the individual objects become magneticallynonadherent and separate from said mass, then positively moving theobjects out of said zone into and through a second zone, inductivelyheating the second zone, and conductively heatin the individual objectsto a predetermined temperature above their Curie points while movingsaid objects through said second zone.

EDGAR L. BAILEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 686,836 Ruthenburg Nov. 19, 1901995,636 Ruthenburg June 20, 1911 1,296,896 Wright Mar. 11, 19191,412,484 Mordley Apr. 11, 1922 1,538,365 Wilison May 19, 1925 1,687,656Brown Oct. 16, 1928 1,732,917 Summey Oct. 22, 1929 1,734,536 Sorrel etal. Nov. 5, 1929 1,747,934 Heidenhain Feb. 18, 1930 1,782,359 LinnhoflNov. 18, 1930 1,799,102 Kelley Mar. 31, 1931 2,286,024 Tama et al. June9, .1942

